onClick doesn't fire with only one input when pressing enter

I'm having trouble with events in Internet Explorer 7.

When I have a form with two or more input[type=text] and I press enter, the events occurs in this order:

1. submit button (onClick)
2. form (onSubmit)

Sample code:

<form onSubmit="{alert('form::onSubmit'); return false;}">
    <input type="text">
    <input type="text">
    <input type="submit" onClick="{alert('button::onClick');}">
</form>

If I have only one input[type=text] and I press enter the submit button onClick event doesn't fire. Sample code:

<form onSubmit="{alert('form::onSubmit'); return false;}">
    <input type="text">
    <input type="submit" onClick="{alert('button::onClick');}">
</form>